Controllers for controlling a starter motor electronically are now conventional. They generally include a control unit which receives as an input a flag concerning the open or closed state of a starter switch--which switch is generally actuated by the vehicle key--and which controls the application of power to the coil(s) of a power contactor which, when closed, serves to power the electric starter motor. The power contactor includes, in particular, a moving core which, at the end of its stroke, closes the power supply circuit for the electric starter motor and whose displacement causes the starter pinion to be entrained towards the ring gear. This control unit also serves to control other functions such as automatically stopping the starter or indeed providing protection against surge currents or against operator error such as trying to start an engine that is already running. The control unit is either integrated within the starter itself, or else it is housed externally thereto in a special box. In another variant it may be constituted by an already-existing electronic system, such as the injection and ignition processor.
It can happen, particularly in the event of some kind of vehicle breakdown, that the user makes numerous successive attempts at operating the starter motor in the hope of starting the engine.
Each time it is activated, the starter motor heats up quickly and its temperature rises significantly--by a few degrees--as a function of its operating characteristics and as a function of the length of time it is activated. The lengths of the pauses between successive attempts at starting are of the order of a few seconds and they enable the starter motor to cool down to some extent. However, its rate of cooling is much slower than its rate of heating, such that as a general rule the starter motor is far from returning to its initial temperature when it is reactivated.
This gives rise to a cumulative heating effect which, if too many attempts are made or if they last for too long, will lead to the starter motor being destroyed.
Unfortunately, it turns out to be impossible to protect the starter motor against being destroyed in that way merely by requiring sufficiently lengthy pauses between two successive closures of the power contactor: the control unit, which is generally constituted by a microprocessor, loses power between two successive actuations of the contact switch, and that makes it impossible to use the internal clock of said control unit for measuring time.